1. Field of the Invention
The present invention relates to a target substance detection material and a target substance detection method, which are used to detect a target substance contained in a specimen.
2. Description of the Related Art
In general, a method for specifically detecting the presence or absence of a target substance contained in a specimen or the concentration thereof using an antigen-antibody reaction, which is known as immunological test or immunoassay, is used in many tests. Examples of a test using such a detection method include: xenodiagnosis for detecting viruses or bacteria causing infectious diseases, or disease marker molecules; environmental inspection for detecting harmful substances such as endocrine disrupting chemicals or dioxins existing in the environment; and food inspection for detecting allergenic substances or bacteria existing in food.
In such inspections, a method for detecting the presence or absence of a target substance or the concentration thereof with high sensitivity by substituting them with the presence or absence of a so-called “labeled form” or the concentration thereof is adopted in many cases. Such a labeled form includes a case of being indirectly detected (indirect labeled form) and a case of being directly detected (direct labeled form). An indirect labeled form is used in the enzyme immunoassay (EIA) method, the chemiluminescent immunoassay (CLIA) method, or the electrochemiluminescence immunoassay (ECLIA) method. That is to say, such an indirect labeled form is used to measure the presence or absence of a substance that is indirectly converted by a labeled form, or the concentration thereof. A direct labeled form is a labeled form used in direct detection of the presence or absence of a labeled form itself or the concentration thereof, such as a case where the labeled form is a fluorochrome or latex label.
In addition, one example of the “labeled form” is an aggregated labeled form. As with colored latex used in the latex assay, the aggregation degree of an aggregated labeled form is increased as the concentration of a target substance is increased. Thus, such an aggregated labeled form is used in a method of detecting the presence or absence of a target substance or the concentration thereof by reading a change in the optical properties thereof.
In recent years, a fine gold or silver particle having a diameter between several nanometers and several hundreds of nanometers has been used for the direct labeled form and the aggregated labeled form among the aforementioned labeled forms.
By an optical effect known as localized surface plasmon resonance, such a fine gold or silver particle having a diameter between several nanometers and several hundreds of nanometers generally has the property of absorbing light between approximately 450 and 650 nanometers, and it is colored in a visible region. It has been known that, with regard to absorption of light due to localized surface plasmon resonance, the strength or absorption wavelength thereof is changed by the positional relationship between fine particles. In addition, when compared with the previously used labeled forms, since such a fine gold or silver particle does not have discoloration towards fluorescent labeling, and also since such a fine particle is very advantageous in that the particle size thereof is smaller than that of latex and in that a reaction efficiency is high, such a fine gold or silver particle has been used as the aforementioned direct labeled form or aggregated labeled form in many cases.
Japanese Patent Application Laid-Open No. H11-032791 discloses a detection method using antibody-sensitized colloidal gold produced by allowing colloidal gold particles to be adsorbed on an antibody. Such antibody-sensitized colloidal gold is prepared, and the antibody-sensitized colloidal gold is allowed to react with an antigen group containing a test antigen. Thereafter, the reaction product is washed, and a red test antigen, to which the antibody-sensitized colloidal gold has been fixed, is detected by visual observation.
Japanese Patent Application Laid-Open Nos. H11-101799 and 2000-146967 disclose a method of enhancing the safety of a reagent solution containing antibody-sensitized metal colloid, which is used in measurement methods such as an immunochromatography method or an agglutination calorimetric method using such antibody-sensitized metal colloid as a labeled form. In the immunochromatography method, an antigen/antibody-metal colloid complex formed by allowing antibody-sensitized metal colloid to react with an antigen is electrophoresed on a determination paper (film). The complex is captured by the antibody immobilized on the determination paper on which an antibody is immobilized, and coloration due to the metal colloid generated as a result of such capture is then determined, so as to examine the presence or absence of an antigen. In the agglutination calorimetric method, a change in color tone generated as a result of agglutination of gold colloid when antibody-sensitized gold colloid is allowed to react with an antigen in a solution is defined as a change in absorbance, and such a change is measured, so as to examine the presence or absence of an antigen or the amount thereof. It is considered that the enhancement of the safety of a reagent solution containing gold colloidal particles used in these methods contributes to the improvement of measurement precision.
Japanese Patent Application Laid-Open No. 2004-325192 discloses a method of measuring a hapten suitable for automation that does not need B/F separation, which has good measurement sensitivity and wherein the measurement time is reduced, and a measurement kit based on the above measurement method. This method of measuring the amount of a hapten in a specimen includes the following steps. First, a specimen containing an antigen is mixed with a first reagent containing a hapten-binding protein. Then, a second reagent containing an antihapten antibody-binding gold colloid is added to the obtained mixed solution, and they are then mixed. Thereafter, a change in absorbance due to an immune agglutination reaction occurring between the hapten-binding protein and the antihapten antibody-binding gold colloid is obtained based on absorbance measured two or more times at a wavelength between 500 nm and 580 nm. Otherwise, such a change in absorbance is obtained based on absorbance measured two or more times at a dual-wavelength, namely, at a dominant wavelength between 500 nm and 580 nm and at a subwavelength between 620 nm and 800 nm.
Japanese Patent Application Laid-Open No. 2004-346177 describes a method of detecting a target substance using an imprinted polymer on which a gold nanoparticle is immobilized. In this detection method, a target substance is detected by utilizing a change in the expansion coefficient of an imprinted polymer generated as a result of the action of the imprinted polymer to capture the target substance. When the expansion coefficient of the imprinted polymer is changed, the distance between gold nanoparticles immobilized on the imprinted polymer is changed, so that signals derived from the gold nanoparticles are also changed. Utilizing such a change in the signals, the target substance can be detected.
Japanese Patent Application Laid-Open Nos. H11-032791, H11-101799, 2000-146967 and 2004-325192 describe test methods, in which the characteristics of the aforementioned fine gold or silver particles are utilized. However, since an antibody acting as a target substance capturing unit is immobilized on the surface of such a fine gold or silver particle in these methods, a phenomenon such as agglutination or precipitation is likely to occur depending on conditions. Such a phenomenon may affect the reproducibility or precision of the test.
In the detection method described in Japanese Patent Application Laid-Open No. 2004-346177, a change in the expansion coefficient of an imprinted polymer obtained when it captures a target substance is small, and thus it is considered to be difficult to conduct measurement with high sensitivity.